java.lang.RuntimeException：无法启动活动ComponentInfo和在Android Studio中调用另一个活动

我是新来的android开发，并尝试创建一个简单的注册应用程序，但每次点击Register Here TextView时应用程序崩溃。除此之外，我编写登录按钮来尝试调用另一个活动，但点击按钮后它没有响应。我很努力地想找到错误，但我不确定在编码中错过了什么。java.lang.RuntimeException：无法启动活动ComponentInfo和在Android Studio中调用另一个活动

这是主要的活动

package com.fyp4201.universityguide; 

import android.content.Intent; 
import android.os.Bundle; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.View; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.widget.TabHost; 

public class MainActivity extends AppCompatActivity { 
TabHost tabHost; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    TabHost host = (TabHost) findViewById(R.id.tabHost); 
    host.setup(); 

    //Tab 1 
    TabHost.TabSpec spec = host.newTabSpec("tab1"); 
    spec.setContent(R.id.tab1); 
    spec.setIndicator("Home"); 
    host.addTab(spec); 

    //Tab 2 
    spec = host.newTabSpec("tab2"); 
    spec.setContent(R.id.tab2); 
    spec.setIndicator("Search Courses"); 
    host.addTab(spec); 

    //Tab 3 
    spec = host.newTabSpec("tab3"); 
    spec.setContent(R.id.tab3); 
    spec.setIndicator("Search University"); 
    host.addTab(spec); 

    //Tab4 
    spec = host.newTabSpec("tab4"); 
    spec.setContent(R.id.tab4); 
    spec.setIndicator("Compare Universities"); 
    host.addTab(spec); 

    //Tab5 
    spec = host.newTabSpec("tab5"); 
    spec.setContent(R.id.tab5); 
    spec.setIndicator("Ranking of Universities"); 
    host.addTab(spec); 


    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
    fab.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
        .setAction("Action", null).show(); 
     } 
    }); 

} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_main, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    switch(item.getItemId()){ 

    //noinspection SimplifiableIfStatement 
     case R.id.action_settings: { 
     return true; 
    } 
     case R.id.action_login:{ 
     Intent intent= new Intent(getApplicationContext(),LoginActivity.class); 
     startActivity(intent); 
    } 
     default: 
    return super.onOptionsItemSelected(item); 
} 
}}

这是登录活动代码

package com.fyp4201.universityguide; 

import android.content.Intent; 
import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 

import android.view.View; 
import android.widget.Button; 
import android.widget.TextView; 

public class LoginActivity extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_login2); 
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    TextView regis = (TextView) findViewById(R.id.register); 
    Button login = (Button) findViewById(R.id.login); 

login.setOnClickListener(new View.OnClickListener() { 

    @Override 
    public void onClick(View v) { 
     Intent intent = new Intent(getApplicationContext(), Homeafterlogin.class); 
     LoginActivity.this.startActivity(intent); 
    } 
}); 


regis.setOnClickListener(new View.OnClickListener() { 

    @Override 
    public void onClick(View v) { 
     Intent intent = new Intent(LoginActivity.this, Register.class); 
     LoginActivity.this.startActivity(intent); 
    } 
}); 

}}

这是注册活动代码

package com.fyp4201.universityguide; 

import android.os.Bundle; 

import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.View; 
import android.widget.EditText; 
import com.android.volley.Request; 
import com.android.volley.RequestQueue; 
import com.android.volley.Response; 
import com.android.volley.VolleyError; 
import com.android.volley.toolbox.JsonObjectRequest; 
import com.android.volley.toolbox.StringRequest; 
import com.android.volley.toolbox.Volley; 
import android.widget.Toast; 
import java.util.HashMap; 
import java.util.Map; 

public class Register extends AppCompatActivity { 
private static final String REGISTER_URL = "http://jrfyp4201.site88.net/volleyRegister.php"; 
public static final String KEY_USERNAME = "username"; 
public static final String KEY_NAME = "name"; 
public static final String KEY_PASSWORD = "password"; 
public static final String KEY_EMAIL = "email"; 
public static final String KEY_CONTACTNO = "contactno"; 

private EditText etname,etuname,etpass,etconpass,etemail,etcontactno; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_register); 
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    etname= (EditText) findViewById(R.id.name); 
    etuname= (EditText) findViewById(R.id.uname); 
    etpass= (EditText) findViewById(R.id.pass); 
    etconpass= (EditText) findViewById(R.id.conpass); 
    etemail= (EditText) findViewById(R.id.email); 
    etcontactno= (EditText) findViewById(R.id.contactno); 
} 

public void onRegisterbtnClick(View view){ 
    registerUser(); 
} 


public void registerUser(){ 
    final String username = etuname.getText().toString().trim(); 
    final String password = etpass.getText().toString().trim(); 
    final String name = etname.getText().toString().trim(); 
    final String email = etemail.getText().toString().trim(); 
    final String contactno = etcontactno.toString().trim(); 

    StringRequest stringRequest = new StringRequest(Request.Method.POST, REGISTER_URL, 
      new Response.Listener<String>() { 
       @Override 
       public void onResponse(String response) { 
        Toast.makeText(Register.this,response,Toast.LENGTH_LONG).show(); 
       } 
      }, 
      new Response.ErrorListener() { 
       @Override 
       public void onErrorResponse(VolleyError error) { 
        Toast.makeText(Register.this,error.toString(),Toast.LENGTH_LONG).show(); 
       } 
      }){ 
     @Override 
     protected Map<String,String> getParams(){ 
      Map<String,String> params = new HashMap<String, String>(); 
      params.put(KEY_USERNAME,username); 
      params.put(KEY_PASSWORD,password); 
      params.put(KEY_NAME, name); 
      params.put(KEY_EMAIL, email); 
      params.put(KEY_CONTACTNO, contactno); 

      return params; 
     } 

    }; 

    RequestQueue requestQueue = Volley.newRequestQueue(this); 
    requestQueue.add(stringRequest); 
} 
}

这是logcat的错误文件

Process: com.fyp4201.universityguide, PID: 20646 
                     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fyp4201.universityguide/com.fyp4201.universityguide.Register}: java.lang.NullPointerException 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2264) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2313) 
                      at android.app.ActivityThread.access$1100(ActivityThread.java:141) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1238) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:136) 
                      at android.app.ActivityThread.main(ActivityThread.java:5333) 
                      at java.lang.reflect.Method.invokeNative(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:515) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:895) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:711) 
                      at dalvik.system.NativeStart.main(Native Method) 
                      Caused by: java.lang.NullPointerException 
                      at com.fyp4201.universityguide.Register.onCreate(Register.java:20) 
                      at android.app.Activity.performCreate(Activity.java:5340) 
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2228) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2313)  
                      at android.app.ActivityThread.access$1100(ActivityThread.java:141)  
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1238)  
                      at android.os.Handler.dispatchMessage(Handler.java:102)  
                      at android.os.Looper.loop(Looper.java:136)  
                      at android.app.ActivityThread.main(ActivityThread.java:5333)  
                      at java.lang.reflect.Method.invokeNative(Native Method)  
                      at java.lang.reflect.Method.invoke(Method.java:515)  
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:895)  
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:711)  
                      at dalvik.system.NativeStart.main(Native Method)

个

寄存器活动的XML文件

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
app:layout_behavior="@string/appbar_scrolling_view_behavior" 
tools:context="com.fyp4201.universityguide.Register" 
tools:showIn="@layout/activity_register"> 

<LinearLayout 
    android:orientation="vertical" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:layout_alignParentTop="true" 
    android:layout_alignParentStart="true"> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Name :" 
     android:id="@+id/textView2" /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:inputType="textPersonName" 
     android:ems="10" 
     android:id="@+id/editname" 
     /> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Username :" 
     android:id="@+id/textView3" /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/edituname" 
     /> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Password :" 
     android:id="@+id/textView4" /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:inputType="textPassword" 
     android:ems="10" 
     android:id="@+id/editpass" 
     /> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Confirm Password :" 
     android:id="@+id/textView7" /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:inputType="textPassword" 
     android:ems="10" 
     android:id="@+id/editconpass" 
     /> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="E-mail address :" 
     android:id="@+id/textView5" /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:inputType="textEmailAddress" 
     android:ems="10" 
     android:id="@+id/editemail" 
     /> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Contact Number :" 
     android:id="@+id/textView6" /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:inputType="phone" 
     android:ems="10" 
     android:id="@+id/editcontactno" 
     /> 

    <Button 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Register" 
     android:id="@+id/registerbtn" 
     android:layout_gravity="center_horizontal" 
     android:onClick="onRegisterbtnClick" /> 
</LinearLayout>

登录活动的XML文件

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
app:layout_behavior="@string/appbar_scrolling_view_behavior" 
tools:context="com.fyp4201.universityguide.LoginActivity" 
tools:showIn="@layout/activity_login2"> 

<LinearLayout 
    android:orientation="vertical" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:layout_alignParentTop="true" 
    android:layout_alignParentStart="true"> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Username" 
     android:id="@+id/textView1" /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/loginuname" /> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Password" 
     android:id="@+id/textView" /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:inputType="textPassword" 
     android:ems="10" 
     android:id="@+id/loginpass" /> 

    <Button 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Login" 
     android:id="@+id/login" 
     android:layout_gravity="center_horizontal" 
     android:clickable="true" 
     android:focusableInTouchMode="false" 
     android:onClick="onLoginClick" /> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:textAppearance="?android:attr/textAppearanceMedium" 
     android:text="Register Here!" 
     android:id="@+id/register" 
     android:layout_gravity="center_horizontal" 
     android:textColor="@color/accent_material_light" 
     android:clickable="true" 
     android:onClick="onRegisterClick" /> 

</LinearLayout>

请告诉我什么，我错过了。谢谢。

来源

2016-09-24 ishidaxkun

检查xml文件中的所有id并在java中更正它们的名称。这似乎是你引用了另一个xml文件的id与这个活动没有关联，就像你可能在注册活动中引用登录xml文件的用户名字段，反之亦然

来源

2016-09-24 20:06:05

感谢您回复我的问题。我检查了XML文件的ID，但在我看来没有错。所有的ID都是独一无二的，指的是正确的活动，或者我错过了一些东西。我应该在这里上传XML文件吗？ – ishidaxkun

Nvm，我解决了这个问题。编码没有问题，只是应用程序在更改后未更新。它在我清理并重建项目之后得到修复。谢谢。

来源

2016-09-26 14:56:13 ishidaxkun

java.lang.RuntimeException：无法启动活动ComponentInfo和在Android Studio中调用另一个活动

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